Six-pascal (0.02-in.-wg) accuracy can be maintained in Biosafety Level 4 laboratories so that, for example, a 50-pascal pressure difference between rooms does not go outside the range of 44 to 56 pascals (0.177 to 0.225 in. wg). In the March article “Biosafety Level 4 Labs Up Close and Personal,” an error was made in converting pascals to inches water gauge.